bai 1:tim x
a)x+x2-x3-x4=0
b)2x3+3x2+2x+3=0
c)x4-2x3+10x2-20x=0
bai 2:tim cap so (x,y) biet
xy+3x-4y=12
bai 3:voi gia tri nao cua x
a)x3-x2+3x-3>0
b)x3+x3+9x+9<0
c)4x3-14x2+6x-21<0
d)x2(2x2+3)+2x2+3>0
bai 4:CMR hieu binh phuong 2 so le lien tiep thi chia het cho 8